1. Field of the Invention
The present invention relates to controlling the cooling rate and cooling time for a hot strip or plate after the final rolling of the hot strip or plate. More specifically, the present invention relates to a model-assisted process for controlling the cooling of the hot strip or plate in controlled rolling and cooling processes where a structure (hot strip or plate) of hardened austenite is final rolled in temperature ranges in which no recrystallization occurs and is cooled in a controlled fashion, in that it is transported at a controlled speed through the cooling device.
2. Description of the Related Art
Optimal quality in microalloyed steels is dependent on the formation of a very fine-grained secondary structure with favorable combinations of properties during the transformation in the cooling line of the austenite that has not recrystallized or has recrystallized only partially. The optimal values for this austenite hardening result from 70-80% reduction at low temperatures (below 900.degree. C.). What is vital is that the hardened state of the deformed and hardened austenite be maintained to the point of the .gamma./.alpha. transformation. Maintaining the hardened state until that transformation depends on the conditions for the precipitation of the microalloy elements and the retardation of recrystallization this causes. In addition to maintaining the hardening of the fine austenitic grains, it is necessary to carry out deliberate cooling, so that the structure obtained after transformation consists for the most part of ferrite and bainite. Pearlitic structures are undesirable. Changes in the final roll temperature during processing and changes in the speed of processing affect the above transformation and change the final ratio of the structural phases of the steel. These changes in the ratio of structural phases of the steel alter the characteristics of the steel. Therefore, a problem with conventional cooling of the final rolled hot strip or plate is that inevitable fluctuations in the final roll temperature and processing speed result in a final product having non-uniform characteristics.